Electrode support element for ceramic discharge lamp

ABSTRACT

An improved electrode support element for ceramic discharge lamps formed from a single refractory metal strip and including at one end a pair of oppositely directed foot portions and at the other end a U-shaped electrode gripping portion with each end interconnected by a relatively rigid blade portion. The foot portions are welded to the inner surface of the refractory metal end closure or cap and provide improved centering and rigidity to the electrode mount.

United States Patent Werner et al.

51 Mar.- 18, 1975 [54] ELECTRODE SUPPORT ELEMENT FOR 3.450.924 6/1969 Knochel et al 3l3/229 X CERAMIC DSCHARGE LAMP 1474.277 10/1969 Zollweg at al. 3l3/28l X [75] Inventors: Leo C. Werner, Cedar Grove, N..l.;

'f f Linv Flu$hmg- Primary Examiner-Siegfried H. Grimm 3 1 Knochel, west Orange Attorney, Agent, or Firm-B. R. Studebaker [73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa ABSTRACT [22] Filed: Mar. 4, 1974 [2]] APPL No; 447,618 An improved electrode supportelement for ceramic discharge lamps formed from a single refractory metal strip and including at one end a pair of oppositely di- Cl 313/218, rected foot portions and at the other end a U-shaped 3 |3/286 electrode gripping portion with each end interconllll. Cl. r nected a relativgly po The foot 1 Field of Search-m 313/217, 213, 327429, portions are welded to the inner surface of the refrac- 313/281, 331, 353, 283-28 tory metal end closure or cap and provide improved centering and rigidity to the electrode mount. [56] References Cited UNITED STATES PATENTS 7 Claims, 4 Drawing Figures 3.422300 l/l969 Knochel et al 313/220 23 3s 5O a: f

ELECTRODE SUPPORT ELEMENT FOR CERAMIC DISCHARGE LAMP BACKGROUND OF THE INVENTION This invention relates to high pressure ceramic discharge lamps and more particularly to an improved electrode support element to provide better centering within the arc tube as well as rigidity to the electrode mount in such a lamp.

In discharge lamps employing the ceramic arc tube the opposed discharge sustaining electrodes are mounted at least at one end of the arc tube to the exhaust and fill tubulation which extends through the end cap or end closure of the arc tube body. Many such lamps employ refractory metal tubulation as the electrode support in both ends of the lamp but such construction involves increased material expenseand additional machining operations as well as an additional seal. This kind of construction not only leads to increased lamp cost but in addition it is well known that one of the most critical problems in lamp failure is imperfect seals and elimination of the tubulation as a support at one end of the arc tube eliminates the requirement for one such seal area. Tubulation is of course required in at least one end of the lamp to provide for the exhausting of the interior of the arc tube and for the introduction of the discharge sustaining fill, such as for example an amalgam of sodium and mercury, and some prior art are tubes. do include tubulation at only one end. Illustrations of non-tubulated end closures employing a completely closed cup-shaped cap may be found in US. Pats. Nos. 3,746,907 and 3,682,525. In the construction illustrated in the aforementioned patents L-shaped electrode support elements were employed on the inner side of the end closure and an L- shaped electrical lead is employed on the outside of the end closure with each of these elements welded to the circular disc-like flat surface of the end cap. Although this construction eliminated the need for an expensive tubulation carrying end closure, problems were encountered in both the spot welding process with which the L-shaped members were attached to the end cap or closure and electrode orientation was difficult to standarize. Because of the L-shaped configuration the electrode could become easily canted with respect to the longitudinal axis of the arc tube placing the hot discharge sustaining electrode nearer to one side of the arc tube body than the other causing a hot spot to occur at the near side wall of the arc tube and in some instances failure. Additionally, when the L-shaped members were spot welded to the thin walled refractory metal end closure, burn through or splash welding could occur causing brittleness and slowly leaking end closures. X-rays of arc tubes fabricated in accordance with the prior art concept illustrate a substantial number of non-centered, canted, electrode mounts and in many cases illustrate electrodes which are canted to such a degree that they actually contact the are tube wall.

SUMMARY OF THE INVENTION The novel improved electrode support element of this invention provides greater rigidity to the electrode mount as well as improved centering of the electrode with respect to the interior walls of the ceramic body. Additionally, the configuration of the electrode support element and the outer lead to the outer surface of the end closure or cap because of their'complementary configurations provide for improved stability of the welds. The foregoing is accomplished inaccordance with the present invention by providing. in a ceramic discharge lamp which conventionally includes a base, an outer envelope sealed to the base and a ceramic arc tube mounted within the outer enevelope and electrically connected to the base, whicharc tube has refractory metal end closures sealing off the ends thereof and carrying on their inner surface a discharge sustaining electrode, the improved electrode support of this invention. The improved electrode mounting and support tab or element is associated with at least one of the end closures and is characterized by a pair of oppositely directed foot portions, a central bladeportion and a U- shaped electrode shank gripping-portion. The pair of foot portions are welded to the inner surface of the end closure to thereby provide both improved centering.

and rigidity to the electrode mount.

BRIEF DESCRIPTION OF THE DRAWINGS Many of the attendant advantages of the present invention will'become more readilyapparent and better understood as the following detailed description is considered in connection with the accompanying drawings, in which:

FIG. 1 is a side elevationalview partly in section of a ceramic discharge lamp employing the improved electrode support element of this invention;

FIG. 2 is an enlarged side elevation, partly in section of an arc tube of the ceramic type employing this invention;

FIG. 3 is a partial sectional view of the upper end cap illustrated in FIG. 2; and,

FIG. 4 is a bottom plan view of'the end cap of FIG.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now in detail to the drawings, wherein like reference characters represent like parts throughout the several views there is illustrated in FIG. 1 a typical high pressure sodium lamp of the ceramic arc tube type generally designated 10. The discharge lamp 10 includes an outer envelope of glass 12 attached to a standard metal mogul base 14. A pair of lead-in conductors 16 and 18 (partially superimposed in FIG. 1) are conventionally connected to the mogul base 14 and extend through a reentrant stem press 20 at the base of the envelope 12 in a conventional manner. Mounted on the upper end of lead-in conductor 18 is the arc tube support frame 22 which serves both to retain and mount the arc tube within the outer. envelope 12 as well as to conduct electricity to the upper electrode of the arc tube. The frame 22 is supportedat its upper end within the envelope 12 by a pair of resilient spring members 24 which serve to retain the frame 22 in a central location within the outer envelope 12 through resilient contact with the inner surface of the outer envelope.

A conventional ceramic are tube 26 preferably of polycrystalline alumina orsapphire is mounted at its lower end to lead-in conductor 16 by means of a flexible wire 31 which encircles the exhaust and fill tubulation 30 of the arc tube and is welded to the lead-in conductor 16. The flexible wire 31 is brazed to the tublation 30 in the manner disclosed in copending application Ser. No. 392,692, filed Aug. 29, 1973 for an'lmproved Ceramic Arc Lamp Construction and owned by the assignee of this application. The tubulation extends through an end cap 32 at the lower end of the lamp which tubulation serves to mount the lower electrode 34 in a manner described in copending application Serial No. 447,619, filed the same date as this application for an Improved Tubulation Design filed by the inventors of this application and owned by the same assignee as this application.

At the other end of the arc tube 26 is a nontubulation carrying end cap or end closure 36. An inverted T-Shaped lead-in conductor 38 including foot or flange portions 39 is spot welded to the outside of the end cap 36 to provide electrical current to the electrode 40 mounted on the inner side of the end cap 36 by the electrode support element of this invention. The lead-in conductor 38 is electrically connected to the support frame by a flexible strap 42 at 44. The strap 42 is welded to the lead-in conductor 38 and to the lateral support bar 46 at their juncture. The lateral support bar 46 has channels therethrough at 48 which surround the vertical arms of the support frame 22 to provide for centering of the upper end of the arc tube with respect to the frame but in a manner which will permit longitudinal expansion of the arc tube through the lose sliding fit relationship between the support frame 22 and the channels or apertures 48 in support bar 46.

As best illustrated in FIGS. 3 and 4 the upper electrode 40 is rigidly mounted and centered with respect to the end cap or end closure 36 by means of an electrode support element 49 formed from a single strip of refractory metal suchas tantalum, niobium or molybdenum and includes a pair of oppositely directed foot portions 50, a central blade portion 52 and a U-shaped electrode shank or rod gripping portion 54. In the past the upper, non-tubulation mounted electrode has been mounted by a simple L-shaped member which was readily susceptible to non-center mountings and angular disposition with respect to the longitudinal axis of the arc tube. The electrode support element 49 of this invention greatly facilitates centering because of the oppositely directed foot portions 50 which support the blade portion 52 on both sides thereof and provides a rigid base for the U-shaped electrode shank gripping portion 54.

The ceramic discharge lamp of this invention is of course filled with a discharge sustaining fill of for example an amalgam of sodium and mercury 58 which is introduced into the arc tube through the tubulation 30 which is then tipped off and sealed as at 60 in FIG. 2. In the preferred embodiment the electrode support element 49 is constructed from a strip of tantalum .010 inches thick, .156 inches wide and 3/8 inch long. Approximately the first third of the strip is bisected to form the leg portions 50 which are bent at right angles to the remainder of the strip and in opposite directions from each other. The upper third of the strip is formed in a semitubular configuration to provide a substantially U-shaped slot into which the shank or rod portion of the electrode 40 is welded. The oppositely directed foot or flange portions 39 of the lead-in conductor 38 coincide with the foot portions 50 of the electrode support element and the respective foot portions are juxtapositioned on either side of the flat end portion of the end cap 36 and welded thereto simultaneously. This improved. welding configuration significantly reduces or eliminates problems caused by burn through or splash welding in the assembly of the end cap 36, its lead-in conductor 38 and electrode mount 49 primarily because of the alignment of the three material thickness between the welding jaws at the point of the welds.

As will be apparent from the foregoing, the improved electrode support element of this invention provides a significantly more rigid electrode support which is more easily centered and more easily welded to the end cap. Furthermore, the improved electrode support element of this invention eliminates the problem of canted electrode mountings which place the electrode too near or in contact with the arc-tube wall causing hot spot lamp failure. The relationship of the electrode support element foot portions with the foot portions of the lead-in conductor leads to an improved weld to the end cap at that end of the lamp eliminating problems of burn through during welding.

What is claimed is:

1. In a ceramic discharge lamp comprising a base, an outer envelope sealed thereto and a ceramic arc tube mounted within said outer envelope and electrically connected to said base, said are tube having refractory metal end closures sealing off the ends thereof and carryingon their inner surface a discharge sustaining electrode, the improvement comprising; an improved electrode mounting and support element associated with at least one end closure, said mountingand support element characterized by a pair of oppositely directed foot portions, a U-shaped electrode shank gripping portion and a central blade portion connecting said foot portions to said U-shaped electrode gripping portion, said pair of foot portions being welded to the inner surface of said at least one end closure to thereby provide both centering and rigidity to the electrode.

2. A ceramic discharge lamp according to claim 1, wherein a T-shaped lead-in conductor including a pair of oppositely directed flange portions complementary to the'foot portions of said electrode mounting and support element is welded at said flange portions to the other side of said end closure opposite said foot portions.

3. A ceramic discharge lamp according to claim 1, wherein said end closure is niobium and said mounting and support element is tantalum.

4. An improved electrode support element for a ceramic discharge lamp, said electrode support element being formed from a single strip of refractory metal and comprising:

an intermediate flat blade portion;

a pair of foot portions at one end of said blade por-' tion extending in opposite directions away from and at right angles to said blade portion; and

a semi-tubular electrode gripping portion at the other end of said blade portion extending linearly therewith.

5. An improved electrode support element according to claim 4, wherein said refractory metal strip is tantalum.

6. An improved electrode support element for a ceramic discharge lamp, said electrode support element being formed from a single refractory metal strip and including at one end a pair of oppositely directed foot portions and at the other end a U-shaped electrode gripping portion with each said end interconnected by a relatively rigid blade portion, said oppositely directed foot portions extending at right angles from said relatively rigid blade portion.

ing at least one of said electrodes to one of said end caps, said electrode support element comprising a blade portion, a pair of laterally extending foot portions connected at one end of said blade portion and electrode gripping means connected at the other end of said blade portion, said foot portions extending in opposite directions away from said blade portion and welded to the inner surface of said end cap. 

1. In a ceramic discharge lamp comprising a base, an outer envelope sealed thereto and a ceramic arc tube mounted within said outer envelope and electrically connected to said base, said arc tube having refractory metal end closures sealing off the ends thereof and carrying on their inner surface a discharge sustaining electrode, the improvement comprising; an improved electrode mounting and support element associated with at least one end closure, said mounting and support element characterized by a pair of oppositely directed foot portions, a U-shaped electrode shank gripping portion and a central blade portion connecting said foot portions to said U-shaped electrode gripping portion, said pair of foot portions being welded to the inner surface of said at least one end closure to thereby provide both centering and rigidity to the electrode.
 2. A ceramic discharge lamp according to claim 1, wherein a T-shaped lead-in conductor including a pair of oppositely directed flange portions complementary to the foot portions of said electrode mounting and support element is welded at said flange portions to the other side of said end closure opposite said foot portions.
 3. A ceramic discharge lamp according to claim 1, wherein said end closure is niobium and said mounting and support element is tantalum.
 4. An improved electrode support element for a ceramic discharge lamp, said electrode support element being formed from a single strip of refractory metal and comprising: an intermediate flat blade portion; a pair of foot portions at one end of said blade portion extending in opposite directions away from and at right angles to said blade portion; and a semi-tubular electrode gripping portion at the other end of said blade portion extending linearly therewith.
 5. An improved electrode support element according to claim 4, wherein said refractory metal strip is tantalum.
 6. An improved electrode support element for a ceramic discharge lamp, said electrode support element being formed from a single refractory metal strip and including at one end a pair of oppositely directed foot portions and at the other end a U-shaped electrode gripping portion with each said end interconnected by a relatively rigid blade portion, said oppositely directed foot portions extending at right angles from said relatively rigid blade portion.
 7. A ceramic discharge lamp including a metallic base, an outer envelope sealed to the metallic base, a ceramic bodied arc tube supported within said outer envelope and electrically connected to said metallic base, said arc tube comprising: a hollow tubular ceramic body, an end cap sealing off each open end of said ceramic body, discharge sustaining electrodes electrically connected through and supported by said end caps, an electrode support element mounting and supporting at least one of said electrodes to one of said end caps, said electrode support element comprising a blade portion, a pair of laterally extending foot portions connected at one end of said blade portion and electrode gripping means connected at the other end of said blade portion, said foot portions extending in opposite directions away from said blade portion and welded to the inner surface of said end cap. 